Installation on Samsung A21S - Requires bootloader with binary version C

if you still have access to SamsungOS, you can use the system updater.

if you don’t, you will need tools,

to flash latest firmware prior to /e/.

what is your “free from carrier” country related CSC ?
600+ Samsung CSC Codes - Complete List (2025) - Technastic
what is your device model-number ?
https://samfw.com/firmware/SM-A217F
https://samfw.com/firmware/SM-A217M